I think it should be Die Erdbeere?
"mit der Erdbeere" is correct. "mit" takes the dative case. Make sure you always read the tips. http://duolingo.com/#/skill/de/Dative-Case (scroll down)
Wow, those tips are so useful. Haven't even noticed them yet. They should made more obvious
It's sort of confusing, but in the dative case, die (singular feminine) --> der by default :)
Yea, that one is confusing, and I knew it...but I forgot. Are there any other weird things about dative?
I liked this, because you can infer the correct answer even without knowing the definite article of Erdbeere